ACCIDENTAL DISPERSAL 
301 
Man has brought the brown and the black rats apparently. 
Why should the agencies of accidental transport have been 
so much more potent in the distant past than they are 
now ? We might add also, is it possible that these same 
agencies should be able to select the most ancient forms of 
life as more suitable for transport than more modern pro¬ 
ductions ? Of course, these ideas of mammals being carried 
across a vast expanse of ocean and safely landed on a distant 
shore are mere conjectures unsupported by any evidence. 
“ Of land-birds,” says Mr. Darwin, “ I obtained twenty-six 
kinds, all peculiar to the archipelago and found nowhere else, 
with the exception of one lark-like finch (Dolichonyx oryzi- 
vorus) from North America.” Of waders and water-birds he 
succeeded in capturing eleven kinds, only three of them being 
new species. In 1875 the number of land-birds known to Mr. 
Salvin had increased from twenty-five to thirty-six species. 
Most of the genera to which they belong are of very wide 
distribution; seven, however, are confined to continental 
America, leaving five peculiar to the islands. Mr. Salvin * 
expresses no doubts as to the correctness of Darwin’s inter¬ 
pretation of the origin of the Galapagos islands. Hence he 
concludes that the birds now foupd on the islands, being 
related to American birds, must have emigrated from'America 
and have become modified by the different climatic condi¬ 
tions with which they were surrounded. A later review of the 
Galapagos birds was undertaken by Mr. Ridgway f in 1897, 
when the number of land-birds recorded from the islands was 
nearly doubled. He notes the exact distribution of the various 
species and varieties in detail, and shows how circumscribed 
their range is. Of the five genera peculiar to the islands 
only two, viz., Nesomimus and Nesopelia are of evidently 
American relationship. The remaining three, he thinks, have 
so obvious a leaning towards certain Hawaiian dicaeidine 
forms, that the possibility of a former land connection with 
the Sandwich islands, either continuous, or by means of inter¬ 
mediate islands as “ stepping stones,” becomes a factor in 
the problem of their origin. “It may be,” he adds, “that 
the resemblance of Cocornis, Cactornis and Camarhynchus 
* Salvin, O., “ Avifauna of Galapagos Archipelago.” 
t Ridgway, R., “Birds of Galapagos Archipelago,” p. 467. 
